The quark-gluon string model: soft and semihard hadronic processes

The basic principles of the quark-gluon string model, a perturbative QCD ap proach to describing hadronic processes, are presented. The relation betwee n the s-channel topological 1/N expansion of the hadron-hadron scattering a mplitude and the t-channel expansion in Regge poles is demonstrated, where N is the number of quark flavors or colors. This approach is used to analyz e soft hadronic processes. The attempts to extend the region of applicabili ty of this model to describe the inclusive spectra of resonances and also s emihard hadronic processes are briefly reviewed. In particular, a new modif ication of the model in which Pomeron exchange is treated as the exchange o f two nonperturbative gluons with dynamically generated mass is discussed. Soft and semihard processes, and also charmed-particle production in hadron collisions, are analyzed in this version of the model. The advantages and defects of this approach compared to other perturbative QCD models are disc ussed. (C) 1999 American Institute of Physics. [S1063-7796(99)00104-7].